The present invention relates to tape storage systems, and more specifically, to detecting damaged areas on magnetic tape.
Timing-based servo (TBS) is a technology which was developed for linear tape drives in the late 1990s. In TBS systems, recorded servo patterns include transitions with two different azimuthal slopes, thereby forming a chevron-type pattern. These patterned transitions allow for an estimate of the head lateral position to be determined by evaluating the relative timing of pulses generated by a servo reader reading the patterns as they are passed over the servo reader. Moreover, a longitudinal position estimate of a magnetic head relative to a tape may be determined from the signal generated by a servo reader.
In a TBS format, the servo pattern is prerecorded in several bands distributed across the tape. Typically, five or nine servo pattern bands are included on a given tape which runs about parallel to a longitudinal axis of the tape. Data is recorded in the regions of tape located between pairs of the servo bands. In read/write heads of IBM linear tape-open (LTO) and Enterprise tape drives, two servo readers are normally available per head module, from which longitudinal position (LPOS) information as well as a position error signal (PES) may be derived. Effective detection of the TBS patterns is achieved by a synchronous servo channel employing a matched-filter interpolator/correlator, which ensures desirable filtering of the servo reader signal.
Estimates of the head lateral and/or longitudinal position with respect to a magnetic tape derived from the servo patterns may be used to determine the location of damaged regions on the magnetic tape. For instance, when a read and/or write error occurs while accessing a magnetic tape media that has been damaged for some reason, analysis can be conducted to locate the area where the tape is damaged on the basis of history information that has been saved on the tape media or a tape drive. However, when the history information is limited or when limited read and/or write operations have been performed on the damaged tape around the area where the error has occurred, conventional products are simply unable to identify the area in which the tape is damaged.
There are cases in which an unpredictable problem caused by the damaged region of the tape is detected after a period of time has elapsed. These unpredictable problems may appear as a write error, a decrease in the amount of writable capacity, a read error occurring while reading written data, or increased latency while reading data. However, by the time these unpredicted problems appear in some cases, the tape is already unloaded from the tape drive and the error information relevant to the tape is lost. In other cases the damaged tape is loaded into another tape drive, whereby the history information relevant to the tape is overwritten and lost. Accordingly, the information is unobtainable in such situations, and conventional products are again simply unable to identify areas in which the tape is damaged.
In an attempt to overcome this inability to identify damaged area(s) on the magnetic tape in such situations, some conventional products conduct diagnostic tests. These diagnostic tests are performed by a tape drive and include actually writing data on the tape in an attempt to locate the damaged area(s) by noting where subsequent errors occur while writing the data. However, data that is already stored on the tape must be read and transitioned to another tape before performing the diagnostic testing may be conducted in order to avoid losing the data altogether. Accordingly, diagnostic testing undesirably increases latency while also consuming additional storage capacity.
It follows that conventional products have been unable to efficiently and accurately locate damaged areas on magnetic tape. A solution to this standing issue is desirable in order to improve data retention as well as management of data storage media.